Do not worry about being dropped. Everyone does. Just race more. There really is no substitute, you just need to learn to hold position and follow a wheel. Club riding teaches you that.
We thought it might be good to have someone at the back giving advice, coaching (I’m a level 3 road and TT), generally looking for hazards and providing encouragement! I started racing the winter series as a fourth cat. I’ve raced Hillingdon at least 60 times in everything from the fourths to vets to E123 thrashfesrs at 29mph.
As for warm ups, normally a good 20 minutes BC world class warm up helps. Starts at Hillingdon are not normally 400 watts or you are gone. I didn’t warm up at all!
As long as you are enjoying it, keep it up. I started aged 45 and never thought I’d race.